1. Field of the Invention
The present invention relates to a paper feeding device having a pickup roller movable upward and downward, and to an image forming apparatus provided with the same.
2. Description of the Related Art
Among paper feeding devices that feed a sheet substance having an image to be read or a sheet substance onto which an image is to be formed, there are ones in which a pickup roller is provided that retreats to a retreat position higher than a maximum loading height of the sheet substances at the time when the sheet substance(s) are set, after the job is completed and so forth and descends to a paper feeding position so as to come into contact with the sheet substance(s) at the time when a paper feeding is in operation. The pickup roller is supported at shaft thereof by an end portion of an arm capable of being swung; and thereby, the pickup roller is caused to be disposed at the retreat position when the arm is disposed at a raised position, and the pickup roller is caused to be disposed at the paper feeding position when the arm is disposed at a lowered position. The lowered position is determined at the time of the arm's downward movement by the height at which the pickup roller comes into contact with the top surface of a bunch of sheet substances loaded, and the raised position is determined at the time of the arm's upward movement by a predetermined height at which a regulatory member that constrains the arm from moving upward is disposed.
The arm moves, being supplied with a driving force from a drive motor, upward and downward between the raised position and the lowered position. To the drive motor is inputted a drive signal to cause the arm to move upward and downward by a predetermined amount at respective preset speeds. The arm is held at the raised position at the time other than when the paper feeding is in operation; however, it can fall down by a small amount from the predetermined raised position due to vibration and/or the like. For this reason, the arm initializes its position by moving upward to the position limited by the regulatory member with a predetermined timing within which the arm is considered to have fallen down from the raised position, and starts moving downward from the predetermined raised position when the paper feeding is brought to operation.
Because there is a demand for the speedup of the time spent from a request for the paper feed until a paper sheet is actually fed at the time of the arm's downward movement, and because rotative torque for the paper feed is necessary when the downward movement of the arm and the rotational movement of the pickup roller operate together, a high speed and more torque are required. Further, among such paper feeding devices are ones in which speeds of the upward movement and the downward movement are the same. On that account, there is a risk that big contact noises may occur accompanying the upward and downward movements.
So, among conventional paper feeding devices is one in which the arm is caused to decrease the speed of its downward motion halfway in the course of its movement from the raised position to the lowered position in an attempt to reduce the contact noise produced at the time when the pickup roller comes into contact with the sheet substance(s) (for example, refer to Japanese Patent Unexamined Publication No. 2001-220026 bulletin).
Nevertheless, the above mentioned conventional paper feeding device is incapable of reducing the contact noise produced when the arm comes into contact with the regulatory member at the time of the arm's upward movement. Additionally, there is also a driving noise that the drive motor itself produces, and loudness of the driving noise varies depending on the rotational speed it drives at; however, conventional paper feeding devices have been incapable of reducing the driving noise of the drive motor.
The present invention is directed to providing a paper feeding device capable of reducing noises such as contact noise and driving noise produced when a pickup roller is moved upward, and an image forming apparatus provided with the same.